The invention relates to a method for operating a motor vehicle with a hybrid drive.
Motor vehicles with hybrid drive have both an internal combustion engine and an electric driving engine. To consume as little fuel as possible, it is hereby desired to use whenever possible only the electric driving engine for operating the motor vehicle or to provide at least a substantial part of the propulsion power by the electric driving engine.
At low ambient temperatures, there is, however, the problem that many components of the motor vehicle do not work efficiently in a cold state. This is especially true for a high-voltage battery for supplying the electric driving engine, because the maximum power that can be drawn in a cold state is significantly less than in a hot state. Also, drive components which need to be lubricated can be operated in cold state only with significant energy losses. This is true in particular for the transmission as a result of the increased viscosity of the transmission oil at low temperatures.
DE 197 01 094 A1 discloses a method in which a coolant of an internal combustion engine is heated to a desired temperature by using a continuous microwave heater. Coolant further flows through a heat exchanger for heating air used for interior ventilation of the motor vehicle. The presence of the microwave heating of the coolant enables the latter to be rapidly brought to its desired temperature so that the waste heat of the internal combustion engine can be used directly for heating other components of the motor vehicle.
It is also known from DE 10 2007 032 726 A1 to use heating resistors to dissipate electric energy, generated in hybrid cars during recuperation mode in the event the battery can no longer absorb more energy, with waste heat being usable for heating components of the motor vehicle, such as engine or transmission.
DE 197 01 094 A1 describes an auxiliary heating for motor vehicles, using a continuous microwave heater for heating a coolant for an internal combustion engine in order to provide sufficient heating output for the interior heating, even when the engine is cold and to bring the engine quickly to operating temperature.
U.S. Pat. No. 7,077,244 B2 discloses a method for starting a motor vehicle, wherein a check is executed before starting the motor vehicle as to whether all the motor vehicle components have reached a predefined minimum temperature. If this is not the case, components that are too cold are preheated and the engine start is permitted only when the predefined minimum temperature has been reached.
DE 2 229 195 A1 discloses a microwave heating for accumulators, with microwaves being radiated directly in the accumulator to bring it to operating temperature.
When hybrid vehicles are involved, there is, however, the problem that in purely electric mode the internal combustion engine does not produce waste heat that could be used for heating other components.